Endoscopes are surgical instruments which by their nature include substantial interior cavities. These cavities are closed by the instrument's outer structure. These instruments are small, quite delicate, and can have pressure-compliant parts. Substantial differential pressure between the contained gases and the outside gases can damage the instruments. For example, if the compliant part is a balloon or flexible membrane, it may be ruptured.
One of the problems, although not the only one, arises when the instrument is shipped by air. The large pressure differential between gases trapped in the instrument and the lesser atmospheric pressure at high altitude is potentially very destructive. In a similar way during gas sterilization, the instrument is subjected to over-pressure and under-pressure cycles. To prevent damage from these circumstances, endoscopes are provided with an off-on valve which is intended to be closed except when substantial pressure differentials are to be expected such as in shipment by air, or during gas sterilization. Proper use of this valve will prevent any such damage, but because it relies on somebody's attention, the risk exists that person may forget to open the valve when the instrument is to be gas sterilized or is to be shipped.
There is yet another risk. Often the instrument will be subjected to both gas sterilization and liquid soak sterilization. In the former procedure, gas should be allowed to enter the cavities. to prevent pressure induced damage. In the latter it should be closed to exclude liquid during soak sterilization. Liquid never should enter the instrument. If it does, it risks loss of optical clarity in the viewing field and/or damage to the mechanical components of the scope. When an "active" vent is used in the sense of a valve which must be opened and closed, the operator needs to remember to close the vent for the soak operation, and sometimes will forget. This risk is averted by this invention.
It is an object of this invention to provide passive vent means for the internal cavities in an endoscope which will always be open to flow of gas inwardly or outwardly, but which is always closed to flow of liquid into the cavities